In a recent production process of a semiconductor element, importance of a processing technique for high density and miniaturization has been increasingly higher. One processing technique, a CMP (Chemical Mechanical Polishing) technique, has been a technique essential for formation of shallow trench isolation (STI), flattening of a pre-metal insulating material or an interlayer insulating material, formation of a plug or an embedded metal wiring, or the like in the production process of a semiconductor element.
A polishing agent most frequently used is a silica type polishing agent containing a particle of silica (silicon oxide) such as fumed silica or colloidal silica as an abrasive grain. The silica type polishing agent is characterized by being high in general versatility, and the abrasive grain content, pH, additives or the like are appropriately selected to thereby enable polishing of broad types of materials including an insulating material and a conductive material.
On the other hand, the demand for a polishing agent containing a cerium compound particle as an abrasive grain, mainly directed to an insulating material such as silicon oxide, is also expanded. For example, a cerium oxide type polishing agent containing a cerium oxide (ceria) particle as an abrasive grain can polish silicon oxide at a higher rate even in a lower abrasive grain content rather than the silica type polishing agent (see, for example, Patent Literatures 1 and 2 below).
In recent years, there has been demanded for achieving further miniaturization of a wiring in the production process of a semiconductor element, and polishing scratches generated in polishing have been problematic. That is, even if fine polishing scratches are generated in polishing by use of a conventional cerium oxide type polishing agent, they have not been problematic as long as the sizes of these polishing scratches are smaller than a conventional wiring width, but it has been problematic in the case where further miniaturization of a wiring is to be achieved.
For solving this problem, a polishing agent has been studied in which a particle of a hydroxide of a tetravalent metal element is used (see, for example, Patent Literatures 3 to 5 below). In addition, a method for producing a particle of a hydroxide of a tetravalent metal element has also been studied (see, for example, Patent Literatures 6 and 7 below). These techniques are for decreasing as much as possible a mechanical action while using a chemical action possessed by the particle of a hydroxide of a tetravalent metal element, thereby reducing polishing scratches due to the particle.
In addition, in a CMP step or the like for formation of STI, performed is polishing of a laminate having a stopper (polishing stop layer containing a stopper material) disposed on the convex region of a substrate having a concavo-convex pattern, and an insulating material (for example, silicon oxide) disposed on the substrate and the stopper so that the concave region of the concavo-convex pattern is filled therewith. In such polishing, polishing of the insulating material is stopped by the stopper. That is, polishing of the insulating material is stopped when the stopper is exposed. The reason for this is because the amount of the insulating material polished (the amount of the insulating material removed) is difficult to artificially control, and thus the insulating material is polished until the stopper is exposed, thereby controlling the degree of polishing. In this case, the polishing selectivity of the insulating material to the stopper material (polishing rate ratio: polishing rate of insulating material/polishing rate of stopper material) is required to be increased. For this problem, Patent Literature 8 below discloses the following: a polishing agent contains a particle of a hydroxide of a tetravalent metal element, and at least one of a cationic polymer and polysaccharides to thereby allow silicon oxide to be polished at a high rate, and is excellent in polishing selecting ratio of the insulating material to silicon nitride. In addition, Patent Literature 9 below discloses the following: a polishing agent containing a particle of a hydroxide of a tetravalent metal element and a polyvinyl alcohol whose degree of saponification is 95 mol % or less is used to thereby obtain a high polishing rate ratio of the insulating material to polysilicon.